The present invention relates to an image forming method and an image forming apparatus, and more specifically, to the control of timing between an image reading means (a scanner) and an image forming apparatus (a printer).
In an image forming apparatus such as a copying machine equipped with an image reading means (a scanner) and an image forming apparatus (a printer), a reading clock of the scanner is sometimes different from a scan-writing clock of the printer in terms of frequency. Namely, the foregoing is an occasion where the scan-reading speed per line of the scanner is different from the image forming speed per line of the printer.
A measure to be taken for the aforesaid occasion used to be one wherein two FIFO (first-in first-out) memories were used to read and write alternately so that the clock frequency difference between the scanner and the printer may be absorbed.
Namely, as shown in FIG. 7, in an image forming apparatus equipped with scanner 10, storage section 20 and printer 30, there are provided FIFO memory 21 and FIFO memory 22 in the storage section 20.
In this structure, operations are conducted in timing shown in FIG. 8(a)-FIG. 8(j). In this case, index signals obtained by detecting scanning light of polygon mirror 33 with index sensor 34 are utilized as SIDX (FIG. 8(a)) in scanner control section 12, and are utilized as PIDX (FIG. 8(e)) in printer control section 31.
The scanner control section 12 generates write enable signal WE1 (FIG. 8(c)) corresponding to writing in FIFO memory 21, and generates write enable signal WE2 (FIG. 8(d)) corresponding to writing in FIFO memory 22.
The printer control section 31 generates read enable signal RE1 (FIG. 8(g)) corresponding to reading out from FIFO memory 21, and generates read enable signal RE2 (FIG. 8(h)) corresponding to reading out from FIFO memory 22.
In this case, when data from scanner 10 is being written in FIFO memory 21, reading out is being conducted from FIFO memory 22 to printer 30, and when data from scanner 10 is being written in FIFO memory 22, reading out is being conducted from FIFO memory 21 to printer 30.
Thus, image forming is conducted while absorbing the clock frequency difference between the scanner 10 and the printer 30 by conducting writing in and reading out alternately, using both FIFO memories.
In the aforesaid technique of FIG. 7 and FIGS. 8(a)-8(j), two FIFO memories are required, which results in a relatively expensive apparatus.
It has therefore been considered that a dual port type FIFO memory which can simultaneously conduct writing in and reading out be used. Each of FIGS. 9(a)-9(g) is a time chart showing the timing in the case where one FIFO memory is used.
Points where the scanner 10 and the printer 30 operate by the use of index signals from index sensor 34 (FIGS. 9(a), 9(b), 9(c) and FIGS. 9(d), 9(e), 9(f)) are the same as those in FIGS. 8(a)-8(j).
In this case, a phenomenon results wherein reading out passes writing in as shown in FIG. 9(g), because write enable WE (FIG. 9(c)) is superposed on read enable RE (FIG. 9(f)) in terms of timing, and the scanner 10 is different from the printer 30 in terms of clock frequency.
In the examples shown in FIGS. 9(a)-9(g), since reading by printer 30 is faster, data on the line that precedes by one line are read at the moment of the passing, thus, continuity of data on one line is lost.
When writing by scanner 10 is faster than reading by the printer, data on the line that follows by one line are read at the moment of the passing, thus, continuity of data on one line is lost.
It is therefore an object of the invention to realize an image forming method and an image forming apparatus which can absorb a difference in clock frequency by using one piece of memory when a reading clock of a scanner and a scan-writing clock of a printer are different from each other in terms of frequency.
The first structure is represented by an image forming apparatus equipped with an image reading means which reads images and generates image data, a memory which can conduct writing and reading of data simultaneously and stores the image data, an image forming means which is driven by a scan-writing clock having a frequency different from that of the reading clock of the image reading means, and forms images by reading the image data stored in the aforesaid memory, and with a timing control means by which timing for writing the image data in the memory from the image reading means and timing for the image forming means to read out the image data from the memory are shifted, and with which an image forming means continuously reads out the image data in predetermined quantity from the memory, wherein the image reading means writes the image data in the memory at a unit of data in the predetermined quantity.
In the invention of the image forming method and the image forming apparatus, contents in prescribed quantity written in a memory are continuously read out at an interval of the prescribed quantity, by shifting timing for writing a memory and timing for reading out from the memory.
Accordingly, it does not happen that an address for writing in and that for reading out agree with each other, or they pass. It is therefore possible to absorb a difference of clock frequency by using one memory, when frequency of a reading clock of a scanner is different from that of a scan-writing clock of a printer.
The second structure is characterized in that the aforesaid timing control means shifts timing for writing the image data in a memory from an image reading means and timing for reading the image data from the memory to the image forming means by the use of index signals generated by an index sensor of the image forming means in the image forming apparatus in Item (1).
By shifting timing for writing in and that for reading out by the use of index signals as in the foregoing, it is possible to absorb a difference of clock frequency by using one memory, when frequency of a reading clock of a scanner is different from that of a scan-writing clock of a printer.
The third structure is characterized in that the timing control means makes timing for writing in and reading out from a memory to be variable in accordance with condition for the image reading means and the image forming means, in the image forming apparatus in Item (1).
By shifting timing for writing in and timing for reading out in accordance with the state of operations of the apparatus, it is possible to absorb a difference of clock frequency by using one memory, and to cope with even in the case of mode change in the apparatus.